为什么Math.Tan(90)提供一个未定义的值? [英] Why does Math.Tan(90) provide a non-undefined value?

问题描述

使用Math.Tan()时，我发现90度的结果不是不确定的.但是是 1.6331779e + 16

While working with Math.Tan() I found that the result for 90 degree is not undefined. But is, inturn 1.6331779e+16

这是应用程序的屏幕截图

Here is the screenshot for the app

这是代码

// convert to degrees
angle = (Convert.ToDouble(op1) * Math.PI / 180);
// write the output
FinalResult.Text = Math.Tan(Convert.ToDouble(angle)).ToString();

为什么会有这样的行为?

Why is such behaviour, is it expected?

推荐答案

计算是使用不完美的浮点数完成的(不是Math.PI始终可以完美地表示为十进制).

The calculation is done with floating point numbers which are not perfect (not that Math.PI can ever be perfectly represented as a decimal anyways).

http://en.wikipedia.org/wiki/Floating_point

更具体地说..

https://math .stackexchange.com/questions/536144/why-does-the-google-calculator-give-tan-90-degrees-1-6331779e16

如果想要四舍五入的结果，请检查输入中是否有类似>89.9999 && <90.00001的内容.请勿将==与浮点值一起使用.

If you want a rounded result then check the input for something like >89.9999 && <90.00001. Don't use == with floating point values.

有关为何不将==与浮点数一起使用的说明，请尝试运行以下示例:

For explanation of why not to use == with floating point numbers, try running this example:

var d = 0.2;
for(double k = 1.0; k<100; k++) {
    var t = 0.2 * k;
    t = t / k;
    Console.WriteLine("{0} == {1} ==> {2}", d, t, d == t);
}

我们将0.2乘以整数，再将其除以相同的整数，然后与0.2进行比较.每次都应该是对的，对吧?它不是.很多时候它返回false.

We're multiplying 0.2 by a whole number, dividing it by the same whole number, and then comparing to 0.2. It should be true every time, right? It's not. Many times it returns false.

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